It is desirable to improve cancer detection, prognostic prediction, monitoring, and therapeutic decisions. For example, when cancer is identified at the earliest stages, the probability of cure is very high and therefore diagnostic screening tests that can detect these early stages are crucial.
One example in which early detection can be beneficial is prostate cancer (PCA). PCA is a leading cause of male cancer-related death, second only to lung cancer (Abate-Shen and Shen, Genes Dev 14:2410 (2000); Ruijter et al., Endocr Rev, 20:22 (1999)). Prostate cancer is typically diagnosed with a digital rectal exam and/or prostate specific antigen (PSA) screening. An elevated serum PSA level can indicate the presence of PCA. PSA is used as a marker for prostate cancer because it is secreted only by prostate cells. A healthy prostate will produce a stable amount—typically below 4 nanograms per milliliter (ng/ml), or a PSA reading of “4” or less—whereas cancer cells produce escalating amounts that correspond with the severity of the cancer. A level between 4 and 10 ng/ml may raise a doctor's suspicion that a patient has prostate cancer, while amounts above 50 ng/ml may show that the tumor has spread elsewhere in the body.
The advent of prostate specific antigen (PSA) screening has led to earlier detection of PCA and significantly reduced PCA-associated fatalities. However, a major limitation of the serum PSA test is a lack of prostate cancer sensitivity and specificity, especially in the intermediate range of PSA detection (4-10 ng/ml). Elevated serum PSA levels are often detected in patients with non-malignant conditions such as benign prostatic hyperplasia (BPH) and prostatitis, and provide little information about the aggressiveness of the cancer detected. Coincident with increased serum PSA testing, there has been a dramatic increase in the number of prostate needle biopsies performed (Jacobsen et al., JAMA 274:1445 (1995)). This has resulted in a surge of equivocal prostate needle biopsies (Epstein and Potter J. Urol., 166:402 (2001)).
Thus, development of biomarkers to detect cancer, with improved sensitivity and specificity is advantageous.